Image:hfspec1.jpg| 400px | right | thumb | Computed regular (non-chaotic) Rydberg atom energy level spectra of hydrogen in an electric field near ''n'' = 15 for magnetic quantum number ''m'' = 0. Each Principal quantum number|''n'' level consists of ''n'' − 1 Degenerate energy level|degenerate sublevels; application of an electric field breaks the degeneracy. Note that energy levels can cross due to underlying symmetries of dynamical motion.
The '''Stark effect''' is the shifting and splitting of spectral line
s of atoms and molecules due to presence of an external electric field
. The amount of splitting or shifting is called the Stark splitting or Stark shift. In general, one distinguishes first- and second-order Stark effects. The first-order effect is linear in the applied electric field, while the second-order effect is quadratic in the field.
The Stark effect is responsible for the pressure broadening